In known seats of that type, the seat back cover covers the entire outer face of the box for the safety device, with the cover being provided with tearable stitching to co-operate with said outer face.
Those known seats suffer from the following drawbacks:
it can be difficult to position the tearable stitching of the cover accurately relative to the outer face of the box, since the cover covers said box completely: if it is poorly positioned, then the safety device runs the risk of operating poorly or even of not operating at all in the event of the vehicle being involved in an accident; and PA1 it is necessary to validate proper operation of the safety device for each model of seat cover that may be installed on the seat back, since the operation of said safety device relies on the cover tearing: given the large number of models of cover that are possible for each model of vehicle, that gives rise to very many tests and is expensive. PA1 the housing is fixed to the frame of the seat back by snap-fastening; PA1 the box of the safety device is fixed to the frame of the seat back by snap-fastening through a passage formed in the housing which receives said box; PA1 the housing which receives the box of the safety device includes a side wall, with the side wall of the box of the safety device being fixed thereto by snapfastening; PA1 the box of the safety device is made of a plastics material, the outer face of the box including at least one groove adapted to break so as to enable said outer face to open in the event of the bag of the safety device inflating; PA1 said groove is generally U-shaped, with a base that is substantially vertical and two side branches that extend substantially rearwards from said base; PA1 the margin of the cover is clamped radially between the side wall of the box of the safety device and the housing which receives said box; and PA1 the box of the safety device includes a peripheral flange which covers the peripheral rim of the housing receiving said box, the margin of the cover being clamped axially between said peripheral rim of the housing and said peripheral flange of the box.